Dieters must generally record either the amounts of foods they have consumed or the caloric content of those foods. One popular type of diet is the so-called "exchange" diet. The exchange diet limits the dieter to a preselected number of units of different food categories during a given day or week.
For example, a hypothetical exchange diet may limit the dieter to two units of fruit, unlimited units of vegetables, two units of milk, two units of bread, three units of fat, an unlimited amount of water, and eight units of protein. Typically, the dieter must also consume a minimum number of units from each of these categories every day. During a given week, the dieter may be limited to four units of eggs, four units of cheese, twelve units of meat, and six units of liver. These weekly limited items are proteins. Thus, when a dieter consumes, under this hypothetical exchange diet, two egg units at the first meal of a diet week, he has reduced his permissible remaining weekly consumption of eggs to two units. In addition, he has reduced his permissible daily consumption of protein to six units.
Maintaining a manual record of the units consumed in each category can be tedious and error-prone. It was thus believed desirable to invent a diet monitor for electronically tracking the dieter's progress.